Membrane electrochemical cells have been studied for several decades but with little industrial interest until the last decade. The recent interest stems primarily from the commercial introduction of perfluorinated ion exchange membranes and their use in electrolytic cells to make chlorine and caustic soda (See Chlorine Production Processes, Noyes Data Corporation, Library of Congress Catalog Card Number 81-2361 ISBN-0-8155-0842-5) and for the electrodialytic conversion of multivalent metal salts. U.S. Pat. Nos. 4,325,792 and 4,439,293 and pending U.S. patent application Ser. Nos. 568,897, filed Jan. 6, 1984 and now abandoned and 665,052, filed Oct. 26, 1984 and now allowed. The ion selective perfluorinated membranes are films and laminates of perfluorocarbon polymers containing sulfonic, carboxylic or other fixed negative charges attached to and distributed in the polymer. These polymers have the extraordinary chemical and thermal stability of perfluorocarbons, such as Teflon.RTM. TFE resins. But where Teflon.RTM. unmodified perfluorocarbon is one of the most hydrophobic substances known, Nafion.RTM., a perfluorosulfonic acid resin, is one of the most hydrophylic. The perfluorosulfonic acid resin absorbs water rapidly at room temperature, in amounts depending upon the number of sulfonic acid groups in the polymer structure, pretreatment of the resin and the electrolytic environment. On absorbing water or polar organics, the volume of the resin increases which results in an increase in the linear dimension of a film, laminate, or membrane of the resin. The linear dimensional change for an unsupported film of a perfluorosulfonic acid resin can vary from about 14% to 17% and for a fabric supported membrane from about 3 to 10% (See Perfluorinated Ion Exchange Membranes, W. F. G. Grot, G. E. Munn and P. N. Walmsley--141st Meeting The Electrochemical Society, Houston, Tex., May 7-11, 1972).
An increase in linear dimensions of a membrane that is sealed to a cell frame of fixed dimensions results in the formation of folds or creases in the membrane. Generally the membrane is spaced close to and sandwiched between the electrodes whereby the folds or creases alter fluids flow in the gap between membrane and electrodes, and if the folds are large enough they form a membrane bridge between the anode and cathode. This membrane bridge can result in electroplating metal in and through the membrane when processing multivalent metal salts the cation of which is electrodepositable on the cathode. Metal plate-through of the membrane can cause electrode arcing and rupture of the membrane. A decrease in linear dimensions of an installed membrane resulting from drying can cause rupture of the membrane and loss of fluids and electrical integrity of the electrochemical cell.
Where a membrane is between a header and a base in fixed positions, the spacing between the membrane and the electrodes must be substantial to accommodate the swelling of the membrane upon hydration so as to avoid contact of the membrane with the electrodes. An example of such an electrolysis cell with a rigidly defined ends of a membrane is shown in U.S. Pat. No. 4,006,067. However, the wide spacing required in such structure is disadvantageous in that it does not give the close spacing which results in a more efficient electrodialysis.
The perfluorinated sulfonic acid membranes used to make chlorine and caustic are preconditioned to a desired level of hydration and ionic form of the membrane and installed between the electrodes in a cell frame in the preconditioned state. Preconditioning the membranes decreases dimensional changes from the as-installed to operating conditions but the membrane must be kept hydrated at all times to prevent shrinkage and rupture of the membrane. When a preconditioned membrane is removed from the cell for reuse, it must be preconditioned to the exact state of preconditioning as first installed to obtain the initial membrane dimensions for reinstallation in the cell frame. Although acceptable cell performance can be achieved in chlorine production by installation of preconditioned membranes, the general utility of membrane cells using the preconditioning method for accommodating linear dimensional changes of membranes is very limited.
For general utility of membrane electrochemical cells, it is preferable that the cell accommodate dimensional changes in the membrane and to permit easy assembly and removal of cell components for maintenance and reuse. Preferably, the cell design would permit installation of the membrane dry at ambient conditions and provide predictable and controllable spacing of membranes and electrodes in a variety of chemical environments and operating conditions and return of the installed membrane to dry ambient conditions for cell maintenance and reuse of the membrane. Heretofore, there has been no satisfactory method for making membrane electrochemical cells which provide for large dimensional changes in the installed membrane, especially perfluorinated membranes. An object of the instant invention is to provide a method for making cylindrical type membrane compartmented electrochemical and chemical reactor membrane cells having two or more compartments that permits installation of membranes dry at ambient conditions, provides for predictable and controllable spacing of membranes and electrodes in a variety of chemical environments and operating conditions and return of the installed membrane to dry ambient conditions for cell maintenance and reuse of the membrane.